1. Field of the Invention
The present disclosure relates to high pressure intensifiers.
2. Description of Related Art
High pressure intensifiers (HPIs) are employed in subsea well control systems to reduce the cost of the umbilical from the control center, which may be several hundred kilometers from the well head. Hydraulic control fluid is fed to the well control system via the umbilical at a pressure lower than that required by the control system. The lower pressure enables the umbilical walls to be thinner, making the umbilical smaller in diameter, lighter and easier to deploy, resulting in major cost reductions.
The HPI is located at the well end of the umbilical and increases the hydraulic pressure to a level required by the well hydraulic control system. An example of an HPI is described in GB-A-2 275 969.
Existing HPIs produce a fixed output pressure as a multiple of the input pressure, e.g. 5000 psi in and 10,000 psi out. This fixed pressure is not favoured by many well operators, because they are concerned, in particular, at the possibility of damage to the downhole safety valve (DHSV) fitted in the well fluid extraction flowline, and the major costs involved in its replacement in the event of damage. The DHSV is sensitive, in particular, to the difference in pressure between the production flowline pressure and the valve's hydraulic operating control pressure (a large difference causing the valve to slam hard when opening or closing) which is exacerbated by the fact that the production flowline pressure tends to fall over the life of the well. Well operators would consider this problem solved if the valve's hydraulic control pressure, typically derived from the output of the HPI, was adjustable, to suit changes in the production flowline pressure.